Hydronic system in -25 Celsius (-14 Fahrenheit)

Hi everyone thanks for such great forum. Hoping someone can give me a hand here. I live in a small 10 unit apartment building originally built in the 1960â€™s. There is a hydronic heating system that works really well *except* when it matters the most! What happens is that when it gets *really* cold outside, meaning when the temperature falls below -25 Celsius (so -13 Fahrenheit), I always wake up in the morning and my apartment is absolutely freezing. Something happens in the night, only when it is super super cold that somehow â€œknocks outâ€ the system. I know that it is only my unit because my buddy lives downstairs in another unit and his heating is fine. The other odd part is that when I turn the thermostat up when this happensâ€¦.nothing happens.

How the problem gets resolved is that I leave for work with the thermostat turned way up and when I get home 10 hours later it is always back on.

I donâ€™t understand what happens to make the system â€œre-startâ€ â€“ BUT I can confirm that before I leave in the morning I go put my hand on the Honeywell valve that is there at what I assume is the main water entry point to my unit from the boiler and it is freezing cold. There is no water there at all. This thing of course is always super hot. I donâ€™t understand the specifics of how the water reaches my unit from the boiler, so I canâ€™t quite understand what is wrong or even what causes the system to â€œre-startâ€

The other day this happened on a Saturday for the first time so I was home and could observe when the system re-starts. I was freezing, but it took about 5 hours from when I woke up freezing cold to when water reached the main valve in my unit, it then took several hours for the apartment to warm. I am very confused about what is going on in the system during those five hours when the thermostat is turned up but no water appears to be at the valve.

The final bit of information that might be useful for anyone that might be able to help me understand what is wrong is that my unit gets very warm and I usually turn down the system at night. I think this might have something to do with it. I am wondering if this can â€œknock-outâ€ the system? I usually turn it down to 15 degrees Celsius (59 F) and go to sleep. Itâ€™s almost like reducing the setting to this temperature somehow causes the system to stop, and that when its super cold, something else happens to completely shut the system down.

Can anyone give me a hand here understanding or have a solution? Of course the worst part about this is that it only does this when itâ€™s *super* cold. I have come to expect that my heating will fail for a day when we are in a cold spell.